1. FIELD OF THE INVENTION
The present invention relates to an apparatus for the measuring of dew points, including a sensor intended to measure a temperature, a chiller block intended for the chilling of a bedewable surface and at least one connecting piece arranged as heat transfer means between chiller block and bedewable surface. The invention relates further to a method of determining dew points.
2. DESCRIPTION OF THE PRIOR ART
A large variety of dew point measuring apparatuses are generally known. Best known is the so-called dew point mirror which includes a mirror polished to a high mirror finish on which the bedewable surface is arranged, whereby the bedewage is detected optically. Such a dew point mirror is disclosed, for instance, in the French publication FR-A-2 044 073. As soon as the bedewage develops, the temperature of the bedewable surface is measured and detected as dew point temperature. The chilling is made by means of a chilling chamber adjoining the dew point mirror including a chilling fluid flowing therethrough. In modern dew point temperature sensors a Peltier element is usually used in the chilling block.
In connection now with dew point mirrors measures have been proposed, allowing an improved visual judging of the time of the bedewage. According to the U.S. publication US-A-2 281 418 the mirror is made to communicate with a chilling element only at its center such that a temperature difference is generated along or over, respectively, such mirror such that the contrast between the initially bedewed area at the center and the other areas of this mirror can be seen clearly. Accordingly, it is exclusively the center of this mirror which acts as bedewable surface.
Apart from mirrors and the accordingly optical recognition or detection, respectively, of the bedewage the bedewing is detected the longer the more by means of electrical signals representing a change of the conductivity, the capacity or the travel time or propagation time, respectively, of acoustical waves. To this end attention is drawn, for instance, to the French publication FR-A 1 128 606. This publication describes, furthermore, that the sensor may be heated by means of a built-in heating element after every measurement made such that the condensate may be removed from the bedewed surface and a subsequent measuring be initiated. Corresponding receiving devices of measuring values are disclosed in the German publications DE-A-3 446 277 and DE-A-1 573 377.
All dew point temperature sensors referred to above include a chilling source, from which the bedewable surface is chilled by heat transmission. Such gives rise to a uncontrollable temperature gradient between the chilling source and the bedewable surface or even on the bedewable surface itself.
Depending on the mechanical arrangement of the temperature sensors the above mentioned uncontrollable temperature gradient between the bedewable surface, the temperature sensor and the chilling source gives rise to a larger or smaller measuring error regarding the dew point temperature. The faster the apparatus is chilled the larger this measuring error grows. Due to a speedy chilling and a large heat transfer from the bedewable surface to the chilling source the bedewable surface is usually undercooled and accordingly an erroneously measure of the dew point temperature is made.